GeorgesLemaître:Life,scienceandlegacy17July1894—22June1966

SimonMiBon

StEdmund’sCollege,UniversityofCambridge

WiththefruiKulcollaboraLonof:RodneyHolder(Cambridge),MichaelRobson(Cambridge),CormacO’Raifeartaigh(WaterfordInst.Technology)

PrincipalsourcesofbiographicalinformaLon:DominiqueLambert(Louvain),UnAtomed’Universe,2000ThomasHerzog(Louvain),2012NussbaumerandBieri,DiscoveringtheExpandingUniverse,2009

25November1915

PrussianAcademyofSciencesAlbertEinstein,age36,aciLzenofSwitzerland,asubjectoftheKingdomofPrussia,

andquiteadandy,unveilsaconsistentsetofgravitaLonalfieldequaLons…(…butonlyaeeraraceagainstLmewithDavidHilbert)

TheLemaîtreFamilyandtheBirthofGeorges,1894Charleroi.TheancestryofGeorgescanbetracedthroughfivegeneraLons:agreatgreatgrandfatherClémentenlistedinNapoléon’sarmyandfoughtatWaterloo.ThefamilywasstronglypatrioLc.Hisparentsmarriedon30August1893.Georgeswasbornon17July1894,thefirstoffoursons.Georges’fatherstartedaglassworksandconductedexperimentsontheindustrialproducLonofglass.YoungGeorgeswasfamiliarwithfieryfurnaceswheredecoraLveglassworkwascreated.

In1910firereducedthefactorytoaheapofashes.TheymovedtoBrussels,wherefathersecuredawell-paidposiLonwithSociétéGénérale

EducaLon1904-10.Age10-16.Enrolledatagrammarschool(LaLnandGreek)runbyJesuits.MakeshismarkasanexcepLonalpupilofmathemaLcs,physicsandchemistry.1910-14.StudiescivilengineeringattheCatholicUniversityofLouvain.

9August1914.HeandhisbrotherJacquesenlist.GeorgesservedonthefrontlineoftheBaBleoftheYser23–30October1914.ThecuriouscaseoftheerrorthatLemaîtrespoBedinamilitarymanual

TheWesternFront1914-18

Aeerfouryearsinthetrenches,GeorgesisacLvelyengagedwhentheBelgianarmybreaksoutoftheYserSalientinOctober1918.

WesternFront1918

1919AwardedCroixdeGuerre,withBronzePalm,forconspicuousbraveyinthefaceoftheenemy

21January1919.WhilesLllinmilitaryuniform,LemaîtrestartshisdoctoralcourseatLouvain.1919-20.CoursesongeneralrelaLvity,organisedbyMauriceAlliaume(1882-1931),whowasresponsibleforintroducingtheideasofGRtoawiderpublicinBelgium.1920.DoctorateinphysicsandmathemaLcs;alicencetoteachinBelgium

TheroadtogeneralrelaLvity,1919–20

October1920.EntersaseminaryoftheArchdioceseofMalines(Mechelen)specialisingin“latevocaLons”forveterans.EstablishesastrongintellectualbondwithCardinalDésiré-JosephMercier(1851-1926).ThelaBerhadstronglyresistedtheGermanoccupaLon,andwasanotedscholarofthetheologicalworksofStThomasAquinas(1225-74).

Seminarian,1920–23

Astrophysics was in its infancy. So was astrophotography.

The Nature of the Universe at the dawn of the 20th century

Mainstream view was that the white nebulae are members of the Milky Way

Cosmology did not exist; no extragalactic distance scale

In London professional astronomy was still dominated by the needs of navigation and time keeping, as well as star positions and stellar motion

SeminarianLemaîtrekeptupwiththelatestdevelopmentsinrelaLvity.From1920thenumberofpapersandbooksonrelaLvitypublishedinEuropeexpanded.LemaîtrestudiedEddington’sMathema'calTheoryofRela'vity(1923)aswellasSpace,TimeandGravita'onintranslaLon(1921)During1921-22hepreparedapersonalmemoirontheEinstein’sphysics,whichhesubmiBedforamajortravelbursaryfromtheMinistryofSciencesandArts.

RelaLvity,1920–22

TheprizejuryawardedLemaître8000Belgianfrancsfortravel.

DominiqueLambert(2000)comments:InaddiLontoallthecoursesoftheseminary,LemaîtredeeplyassimilatedinrecordLme,lessthanthreeyears,themostfundamentalaspectsofrelaLvity.InaddiLon,hebecameadequatelypreparedtomeetoneofthefewwho….managedtosummariserelaLvityinarigorousandconcisemanner:Eddington

AmostaccomplishedrelaLvist,1923

In1923Lemaîtresuccessfullyappliedforathree-yearoverseasFellowshipfromtheCommissionfortheReliefofBelgium.

Einstein:HadappliedGRtotheenLreuniverse:staLcuniversewithacosmologicalconstant(forstability).Re-inventscosmologybydoingso!DeSiBer:HadcommunicatedsoluLontoEddingtonforMNRAS:emptyuniverse,zeropressure,closed.Curiousproperty:lightredshieedthelargerthedistancebetweensourceandobserver.Einsteinrejectsthismodel“doesnotcorrespondtophysicalreality.”

SoluLonsofEinstein(1917),anddeSiBer(1917)

Einstein,Ehrenfest,WillemdeSiBer,EddingtonandLorentz.Leiden1923

Friedman(1882–1925):HadcompletemasteryofGRby1922.ProducesasuiteofsoluLons,includingcyclicaluniversesaswellasexpandinguniverses.HispaperinZeits.fürPhysik(1922)ismathemaLcsratherthanphysics.NoconnecLonwithobservaLons.Inpopularbook(1923,Russian)elaboratesonexpandingmodelsoftheuniverse.

MostpuzzlingthingaboutFriedman’spaperisthatithadnoimpactwhatsoeveronthedevelopmentofcosmology,eventhoughtheauthorwasveryclearabouttheexpansionoftheuniverse.Hediedoftyphusin1925.

SoluLonofFriedman(1922)

CambridgeOctober1923–June1924LemaîtrearrivedinCambridgeon3October1923,tendaysaeerordinaLon.HeresidedatStEdmund’sHouse,aresidenLalcommunityofyourCatholicpriestsfromthearchdioceseofWestminster.HerehecombinedthereligiouslifewithninemonthsofdevelopingrelaLvityundertheguidanceofEddington.

Phil. Mag. 48, July 1924 [ 164 ]

XIX. The Motion of a Rigid Solid according to the Relativity Principle.

By G. LEMAITRE, D. es Sc. ( Louvain) *

SINCE previous work on Lemaitre’s problem - intermediate between the special and general relativity theories - is

probably not very familiar to English readers, a brief introduction may be desirable. Simultaneity is relative: but relative

to what?

In the special theory it is relative to a uniformly moving particle, it being assumed that we have a means of fixing

constant orientation in space- or, to combine the two conditions, relative to a '' Galilean " frame of axes. To

materialise the Galilean frame, we must substitute a rigid solid.

This invites a generalization of the definition of simultaneity, so that we may consider simultaneity relative to a generally

moving solid. Lemaitre shows, in certain cases the resolution into space and time separately gives a three-dimensional

space which is curved.

* Communicated by Prof. A. S. Eddington, F.R.S.

1924FirstpaperonrelaLvity:makesanoriginalcontribuLon

6–13August.LemaîtreandEddingtonparLcipateintheBriLshAssociaLonfortheAdvancementofSciencemeeLnginToronto.EddingtongaveanacclaimedpubliclectureonrelaLvityandthebendingofstarlight.LemaîtrelearnsfromLudwigSilberstein(18742–1948;textbookauthor)moreabouthowtheproperLesofadeSiBeruniverse(1917,nomaBer,staLc)canberelatedtoastronomicaldatasuchasredshies.WithinayearLemaîtrewillabandonstaLcsoluLons.LemaîtrevisitsDominionObservatory,OBawa(1902–70).ForconversaLonswithformerastronomerofBelgianRoyalObservatoryaboutCepheids.

Toronto,Canadasummer1924

InSeptember1924LemaîtrearrivedatHarvardCollegeObservatory,thankstohisFellowship.WorkedoncepheidsunderHarlowShapley.HeregisteredasadoctoralstudentwithMIT

1924–25,HarvardCollegeObservatoryandMIT

23–24April1925.ABends133rdConferenceAmer.Phys.SocinWashington.ReadspaperondeSiBer’scosmology.Spring1925.ABendsmeeLngatNatl.Acad.Sci.tohearHubble’spresenLononCepheidsanddistancetoM31.

In May 1925 pays visit to Hubble 1920s,Hubblemeasuresthedistancestonearbygalaxies,usingSlipher’ssampleofobjectswithredshies

EdwinHubble1889–1954

VestoSlipher1875–1969

AndthengoestoLowelltomeetSlipher

Lowell Observatory, Flagstaff, Arizona. Dome and 24-inch telescope

By 1923 the velocity sample was 41, 36 of which were from Slipher

8July1925,returnstoteachingduLesatLouvain.HeconLnuestoworkonmodelsoftheuniverse.HisstarLngpointsare:ForastaLcgravitaLonalfieldwithsphericalsymmetryontwosoluLonsexist:thereisnohappymeanbetweendeSiBer’semptyuniverse(whichaccountsforredshies)andEinstein’suniversewithmaBer.Hesearchedforanintermediatemodel:auniversecontaininggalaxies(Einstein)andwithredshies(deSiBer)

1925-26Louvain:Towardsthefireworksuniverse

ApromisingfeatureofthemodelwastheintroducLonofaposiLvecosmologicalconstant,seenasperformingtheroleof“cosmicrepulsion.”

Thisrequiredtheboldstepofallowingtheradiusoftheuniverse(i.e.space)tovaryinanarbitraryway.IntroducesanewmetricfordeSiBerspace.Thiswouldbeadopted20yearslater(1948)byBondi,GoldandHoyle

1925-26Louvain:Towardsthefireworksuniverse

LemaîtrereturnedtoMITfortheacademicyear1926–27EddingtonhadsuggestedtohimlookingforanexplanaLonofSlipher’sresultsbyexaminingtheeffectsofthecurvatureofspace-LmeinadeSiBeruniverse.OnreturntoBelgiumhewishedtotakeaccountoftheavailabledatabyusingnewcosmologicalsoluLons.Andhereiswhathappenednext…

1926–27.BacktoMITtostudythenewdata

AnnalesdelaSociétéScien'fiquedeBruxelles47A,pp.49–59(1927).

Lemaîtrehasre-discoveredandformalisedtheFriedmanmodels.ForthefirstLmeherelatesthesetoalready-publisheddataontheexpandinguniverse.

Lemaître’s1927paper!

RecepLonofthe1927paperwasinsignificant

LemaîtrehasdiscoveredthefundamentalconnecLonbetweengeneralrelaLvityandcosmology.HeevenmanagedtogetavaluefortheHubbleconstant.Thejournalinwhichhepublishedwasnotobscure

AccordingtoJean-PierreLuminet(2013)thebarriertoacceptancewasrejecLonbyEinstein(1927)andHubble(1929),neitherofwhomwouldacceptanon-staLcmodel.

SolvayConf1927

Friday,10January1930:EddingtonbacksLemaître

AttheOrdinaryMeeLngEddingtonanddeSiBerdiscussedtherecessionvelociLesofgalaxies.Eddington:“ShallweputaliBlemoLonintoEinstein’sworldofinertmaBer,orshallweputaliBlemaBerintoDeSiBer’sPrimumMobile?”

EddingtonanddeSiRer Cambridge1930

FromMay1930,EddingtonanddeSiBerenthusiasLcallypromotedLemaître.EddingtonpublishedatranslaLonofthe1927paperinMNRAS.Curiously,thecalculaLonoftheHubbleconstantwasmissing:Lemaître,perhaps“fearingbeinghissedoffthestage”removeditinproof.

Nature127,706(9May1931)TheBeginningoftheWorldfromthePointofViewofQuantumTheory.G.LEMAÎTRESIRARTHUREDDINGTONstatesthat,philosophically,thenoLonofabeginningofthe

presentorderofNatureisrepugnanttohim.Iwouldratherbeinclinedtothinkthat

thepresentstateofquantumtheorysuggestsabeginningoftheworldverydifferent

fromthepresentorderofNature.Thermodynamicalprinciplesfromthepointofview

ofquantumtheorymaybestatedasfollows:(1)Energyofconstanttotalamountis

distributedindiscretequanta.(2)ThenumberofdisLnctquantaiseverincreasing.If

wegobackinthecourseofLmewemustfindfewerandfewerquanta,unLlwefind

alltheenergyoftheuniversepackedinafeworeveninauniquequantum.

1931ThePrimevalAtom,LeBerstoNature

September1931:BriLshAssociaLonfortheAdvancementofScience

LemaîtreparLcipatedinadiscussionoftheevoluLonoftheuniversethattookplaceinCentralHallWestminsteraspartofthe100thAnniversaryMeeLngofBAAS.

SirJamesJeansJ.Jeans,A.Eddington,W.deSiBer,andE.A.Milneengagedinthis,aswellastheBishopofBirmingham(MathsTripos,Cambridge).

EdwardArthurMilneLemaîtremadeastrongpitchforthedisintegraLonofaprimevalstomasthestarLngpointoftheuniverse.FromthisLmehebecameanexoLcmediacelebrity,parLcularlyinAmerica,towhichhemademanytrips.

FatheroftheFireworksUniverseisFatherLemaître!

1933,Lemaître’squantumcosmology–fossilradiaLon

LemaîtrereplacedthesingularityofLmezerobyasingleatomthatcontainedallmaBerandenergy.AttheLme,radioacLvedecaywasahottopic.So,theprimevalatomcouldhavestarteddisintegraLng,releasingenergy.Hespeculatedtherecouldbefossilrelics.Hesuspectedcosmicrays.Hesuggested;“…thecosmologicalconstantλ…correspondstoanegaLveenergyofvacuum.”–darkenergy!

Concludingremarks:Lemaître’slegacy

1948.Steady-statecosmology.Bondi,Gold,Hoyle1948Alpher&Herman;CMBT=5K1949Hoyle“akindofBigBang…”1955GamowNBC/BBCbroadcast:scoffsatHoyle1965CMBdiscovered.Steadystatedoomed1998DarkEnergy21stcenturyCosmologicalconstant